Sunday, September 28, 2008

Lesson 15: Speed, Time, and Distance....

Distance, Time, and Speed (DTS) Calculations

For a variety of navigation problems, we need to know how to solve for speed, time, and distance. The basic DTS60 expression has it all. By knowing at least two values for Time, Speed, and Distance values in relation to 60 minutes, we can solve for any unknown value.

Formulas: S = (D X 60)/ T T = (D X 60)/S D = (S X T)/60

Need to Know

One degree of indicated latitude is equal to sixty (60) nautical miles in distance. Each degree is divided into sixty (60) minutes, with each minute equal in distance to one (1) nautical mile. As already mentioned, each minute is then divided into tenths (or seconds).

To measure the distance between two positions on a chart or points is to compare this distance to an adjacent latitude scale. Distances in nautical miles or fractions of a mile can be directly read from the indicated degrees, minutes, and tenths of latitude.

Remember DTS60 for Distance, Time, and Speed calculations. For example, to determine a vessel’s Speed, first calculate Distance traveled (set dividers to adjacent latitudes for distances) divided by the amount of time (in minutes) needed to traverse the indicated distance. In other words, Speed is equal to Distance multiplied by 60 divided by Time (S = D X 60 / T). Time traveled is equal to Distance multiplied by 60 divided by Speed (T = D X 60 / S). Distance traveled is equal to Speed multiplied by Time divided by 60 (D = S X T / 60).

Time values must be expressed in total number of minutes not hours and minutes. Therefore we need to use 24 hour time. For example, 2 hours and 34 minutes is expressed as 154 minutes. Learn to use 24 hour or military-time, TRY TO remember that there are only 60 minutes in an hour when doing time calculations not 100 minutes !!!!